Cryostats are used to cool sensors (often referred to as cryogenic detectors or cryodetectors) that are based on a low temperature effect. These cryostats have typically included a first cooling means, as well as a second cooling means that is pre-cooled by the first cooling means. The sensor is thermally coupled to the second cooling means. In order to generate a temperature of approximately 4° K (degrees Kelvin), the first cooling means typically consists of a coupled nitrogen/helium cooler. The second cooling means requires more space and involves more complex processes. The liquid coolant (nitrogen, helium) used by the first cooling means is both expensive and not available in every location. For this reason, the use of sensors based on a low-temperature effect is relatively expensive and generally unsuitable for industrial purposes.
Another cooling means for a cryostat involves a refrigerating machine having the form of a pulse-tube cooler. Such a pulse-tube cooler is described in Info-Phys-Tech No. 6, 1996, from VDI Technologiezentrum, Physikalische Technologien. The pulse-tube cooler includes a pulse tube with a cold heat exchanger at one end and a hot heat exchanger at the other end. The cold head exchanger absorbs heat from the outside, and the hot heat exchanger releases heat to the outside. The refrigerating machine also includes a regenerator that serves as an intermediate heat reservoir, and a pressure oscillator that generates periodic pressure changes. At the end where the cold heat exchanger is located, the pulse tube is connected to the pressure oscillator. Lines connect the pulse tube to the pressure oscillator through the regenerator so that the working gas is periodically shifted between the pulse tube and the pressure oscillator.
A cryodetector with a pulse-tube cooler is described in U.S. Pat. No. 6,230,499, which is related application of European Patent EP 1014056 A2. The cryodetector includes a first cooling means in the form of a two-stage pulse-tube cooler and second cooling means in the form of a demagnetization stage. A 3He/4He dilution refrigerator or a 3He cooler can be used for the second cooling means. Pre-cooling to approximately 4° K is performed by the pulse-tube cooler. Further cooling to the operating temperature of the sensors based on a low-temperature effect in a range of 50-400 mK is performed by the second cooling means.
The price of such a cryodetector device is considerable as a result of the complexity of the apparatus with the two cooling stages and extremely low operating temperatures. In addition, the diameter of the measuring probe is large to accommodate several infrared filters and shields around the probe, which are necessary due to the low operating temperatures.
A cryogenic detector device is sought that is less complex and costly and that has a smaller measuring probe.